An optical fiber, for example, a polarization-maintaining optical fiber generally has a core and stress applying member within cladding. Known aligning methods used when fusion-splicing a pair of such optical fibers to each other are described in below-mentioned Patent Literatures 1 and 2.
The aligning methods described in these publications arrange end faces of a pair of optical fibers so that they are faced toward and spaced away from each other, take images of the vicinities of the end faces from a side thereof with a camera, process the taken images, display the processed images, and conduct the alignment according to the displayed images.